BMR Calculator Direct Overview
Calculate your Basal Metabolic Rate (BMR), which represents the energy your body requires to function at complete rest. Uses Mifflin-St Jeor or Katch-McArdle equations to establish your baseline metabolic floor.
Energy Balance
BMR Calculator
Calculate your Basal Metabolic Rate (BMR), which represents the energy your body requires to function at complete rest. Uses Mifflin-St Jeor or Katch-McArdle equations to establish your baseline metabolic floor.
System Units
Awaiting Calculator Inputs
Fill in the fields above and hit Calculate to generate your body composition targets.
Formula & Math
Uses Mifflin-St Jeor by default, switching to Katch-McArdle if body fat percentage is supplied.
How to Interpret
BMR is your baseline calorie burn. Multiplied by your activity level, it determines your TDEE (maintenance calories).
Plan Integration
Take these estimations back to the main Strategy Finder assessment, or save them in your tracking logs in the local dashboard.
BMR: Basal Metabolic Rate resting metabolism
Science & physiological analysis for strategy selection
Reviewed by BodyCompOS Review Board
Last updated: June 27, 2026 · BodyCompOS Editorial Board
Basal Metabolic Rate (BMR) represents the absolute minimum number of calories your body requires to perform basic life-sustaining functions at rest. This includes respiration, circulation, body temperature regulation, cell production, nutrient processing, and brain activity. BMR represents the largest component of TDEE (typically 60-70%), making it the foundation for all daily energy expenditure calculations and dietary planning.
1. How to Use & Apply This Target
Input your sex, age, height, and weight. BMR represents the lower boundary for calorie targets; you should never consume fewer calories than your BMR for extended periods without medical supervision. Use your BMR to calculate your maintenance TDEE by applying activity multipliers.
2. Mathematical Assumptions & Formula Logic
This calculator uses the Mifflin-St Jeor equation by default. When body fat percentage is provided, it switches to the Katch-McArdle formula, which uses lean body mass directly: `BMR = 370 + 21.6 * Lean Mass (kg)`. This approach provides improved accuracy for individuals with high muscle mass.
3. Step-by-Step worked Mathematical Example
Frequently Asked Questions
Q:Does age affect my BMR?
Yes. BMR naturally declines by roughly 1-2% per decade after age 20. This decline is primarily due to a gradual loss of skeletal muscle mass (sarcopenia) and age-related changes in metabolic tissue activity. Maintaining muscle mass through resistance training helps defend BMR.
Q:Can I increase my BMR?
Yes. The most effective way to increase your BMR is to build skeletal muscle mass (lean body mass). Muscle is more metabolically active than fat tissue at rest, burning roughly 13 kcal per kg per day, compared to fat which burns about 4.5 kcal per kg per day.
Related Strategy Tools
TDEE Calculator
Estimate Total Daily Energy Expenditure, Basal Metabolic Rate (BMR), and maintenance calories using Mifflin-St Jeor BMR, refined with Katch-McArdle when body fat is available. TDEE is the starting foundation for all calorie planning, fat loss, and muscle gain strategy.
Calorie Calculator
Calculate daily calorie targets for fat loss (cutting at a moderate 15% deficit), lean bulk (8% surplus), aggressive bulk (15% surplus), or recomposition (98%). Moderate ranges optimize fat mobilization and muscle retention.
Macro Calculator
Determine daily protein, fat, and carb targets aligned with calorie goals. Sets protein first (1.9 g/kg), dietary fat at 28% of calories, then allocates remaining calories to carbohydrates. Practical macro planning for body composition diet adherence.